But it’s not like he’s six or something ... he was 3 at the end of January. He can just read.
I'm not saying it will work for everyone, but it worked for me - and was easy. Also, there wasn't any "resistance" or sad feelings on the part of the grandkids - they felt good about their choice.
I read the book to them ( whenever I read their other books ) and put a kiddie potty chair in the bathroom. They trained themselves. These books have probably been out of print for over 20 years ( who knows?)- but it would be worth an internet search to try to find one.